Fuel cell power plants for producing electricity from a hydrocarbon fuel are well known in the art and generally consist of a fuel cell stack and a fuel processing apparatus. The fuel cell stack electrochemically converts a hydrogen-rich product gas and an oxidant into electricity. The fuel cell stack has individual fuel cells aligned in series. Each fuel cell is formed by an anode, a cathode, and an electrolyte disposed therebetween. Both the anode and the cathode utilize various well known catalysts. The fuel processing apparatus and the anode are in fluid communication, such that the hydrogen containing product gas is supplied to the anode where the product gas is electrochemically reacted. The product gas containing unused hydrogen is vented from the anode as an anode exhaust. The cathode, which is in fluid communication with an oxidant source, is supplied with an oxidant, usually in the form of Oxygen. At the cathode, the oxidant is electrochemically reacted.
The fuel processing apparatus steam reforms a hydrocarbon fuel and steam into the product gas in order to increase the hydrogen content in the product gas. The product gas is then fed to the fuel cell stack. The steam reformation process is accomplished by contacting the hydrocarbon fuel and steam with a heated catalyst.
The fuel processing apparatus has a furnace which is the heat source for the reformation process and at least one catalytic reactor disposed within the furnace. The furnaces useful for practicing this fuel processing are conventional and typically comprise a shell or housing, air and fuel inlets for introducing air and fuel, respectively, into the furnace shell, as well as, an exhaust port for removing the combustion gases which results from the ignition of the two gases. The catalytic reactors used are also conventional and have an inlet for introducing the hydrocarbon fuel and steam into the catalytic bed to effect the steam reformation.
In operation, the air and the furnace fuel are introduced into the furnace using the air and fuel inlets, respectively. The air may be supplied as compressed air or oxygen, whereas, the furnace fuel may be introduced directly from a fuel source or from the anode exhaust of a fuel cell which contains excess hydrogen not reacted within the fuel cell. Within the furnace, the furnace fuel is burned by a conventional means thereby producing the combustion gases. The combustion gases then flow along the outside of the catalytic reactor to heat the catalyst bed therein. The hydrocarbon fuel and steam enter the reactor through the reactor inlet and flow through the catalyst bed in the reactor. Typically, the flow of the hydrocarbon fuel and steam through the catalyst bed is counter-current to the flow of the combustion gases. The heat from the combustion gases is transferred to the hydrocarbon fuel and steam. This heat transfer relationship drives the steam reformation process within the catalytic reactor between the hydrocarbon fuel, steam and the catalyst, thus producing the hydrogen-rich product gas. After the heat transfer relationship between the combustion gases and the catalytic reactor, the combustion gases exit the shell through the exhaust port. The product gas exits through the reactor exit.
Significant cost savings can be achieved by decreasing the number and/or size of the catalytic reactors, not only by decreasing the amount of expensive materials necessary to build the reactor, but also by decreasing the necessary amount of expensive catalyst necessary to run the reactor. It is well known in the art that the size and/or number of catalytic reactors can be reduced by increasing the flame temperature. The flame temperature is the temperature at which the furnace fuel and air burn. The flame temperature can be increased by increasing the temperature of the air and/or the furnace fuel prior to their introduction into the furnace shell. Conventional fuel processing apparatus utilize a furnace and a heat exchanger separate from the furnace to heat the air or the air and furnace fuel prior to their introduction into the furnace. Flame temperatures utilizing a heat exchanger separate from the furnace to preheat the air are approximately 2200.degree. F. However, this conventional design requires an expensive heat exchanger and does not minimize heat losses due to the transfer of combustion gases from the furnace to the heat exchanger. Therefore, scientists and engineers have been searching for an inexpensive and efficient method and apparatus to increase the temperature of the furnace fuel and/or air prior to their introduction into the furnace.